The present invention relates to a newly stabilized HMG-CoA reductase inhibitor which is used in a pharmaceutical formulation being particularly suitable for the treatment of hypercholesterolemia and hyperlipidemia. More precisely, the present invention relates to a stabilized and very homogeneous composition mixture comprising a HMG-CoA reductase inhibitor, such as atorvastatin, pravastatin, fluvastatin and cerivastatin, or pharmaceutically active salts thereof, as well as solid pharmaceutical formulations containing the aforementioned homogeneous composition mixture as an active substance.
Lovastatin, pravastatin, simvastatin, mevastatin, atorvastatin, fluvastatin and cerivastatin, derivatives and analogs thereof are known as HMG-CoA reductase inhibitors and are used as antihypercholesterolemic agents. The majority of them are produced by fermentation using microorganisms of different species identified as species belonging to Aspergillus, Monascus, Nocardia, Amycolatopsis, Mucor or Penicillium genus. Some are obtained by treating the fermentation products using the methods of chemical synthesis like simvastatin or they are the products of total chemical synthesis like fluvastatin, atorvastatin and cerivastatin.
The purity of the active substance is an important factor for manufacturing a safe and effective pharmaceutical formulation. Maximum possible purity of the product is of particular importance if the pharmaceutical product must be taken on a longer term basis in the treatment or prevention of high cholesterol levels in blood. Accumulation of impurities from drugs of a lower level of purity may cause a variety of side effects during treatment. Besides impurities, that cannot be completely eliminated in the process of preparation of the active substance, degradation products occurring by subjecting the final pharmaceutical formulation to various environmental factors such as temperature, moisture, low pH, carbon dioxide from the air and light, may also impose a significant problem. HMG-CoA reductase inhibitors occurring in the form of salts in the final pharmaceutical formulation, such as atorvastatin, pravastatin, fluvastatin and cerivastatin, are particularly sensitive to an acidic environment in which hydroxy acids are degraded into a lactone.
Apart from the fact that the aforementioned active substance may be destabilized by the environmental factors, their degradation may also be accelerated by interactions with other pharmaceutical ingredients, such as fillers, binders, lubricants, glidants and disintegrating agents. Therefore, the pharmaceutical ingredients and the process for preparation of the pharmaceutical formulation should be meticulously chosen to avoid the aforementioned undesired interactions and reactions.
The stability of the active substance in an acidic environment is one of the major problems in the case of statins in the form of salts. One of possible solutions of the aforementioned problem is described in EP 0 336 298, disclosing a stable pharmaceutical formulation for pravastatin. The essence of the formulation is to maintain an alkaline environment so that the aqueous dispersion of the pharmaceutical formulation reaches a pH above 9, preferably about 10. In addition to the active substance pravastatin, the composition of the invention includes a basifying agent, such as magnesium oxide, which imparts a pH to an aqueous dispersion of the aforementioned formulation above 9. In view of the stability of the active substance such a formulation is effective. However, the local alkaline environment occurring at the site of dissolution of the pharmaceutical formulation may have a negative impact on the gastric mucosa with its normally acidic environment, especially since a relatively high amount of basifying agent is necessary to ensure acceptable stability. This negative impact may be particularly evident for patients with a damaged gastric mucous membrane where the mucosa per se is not able to create a sufficient acidic environment inside the stomach for normal digestive functioning. It is particularly important in chronic therapies as in the case of prophylaxis or treatment with HMG-CoA reductase inhibitors.
Another approach; for providing a stable pharmaceutical formulation is described in the present Applicant""s earlier PCT application No. PCT/IB99/01749.
It is an object of the present invention to provide a pharmaceutical formulation containing as an active substance a HMG-CoA reductase inhibitor which exerts an excellent stability while avoiding the afore mentioned disadvantages. It is a particular object to provide a stabilized active substance as such, i.e. before being formulated into the pharmaceutical formulation, where the HMG-CoA reductase inhibitor is precautionary protected from being degraded.
It is a further object to provide a process for the preparation of a stabilized HMG-CoA reductase inhibitor which exerts an excellent stability while avoiding the afore-mentioned disadvantages.
These and further objects are accomplished by the present invention.
According to the present invention, there is provided a a composition comprising a homogeneous mixture of a HMG-CoA reductase inhibitor with a buffering substance or a basifying substance, which composition has been obtained by co-crystallization and/or co-precipitation of said HMG-CoA reductase inhibitor and said buffering substance or basifying substance.
By means of co-crystallization and/or co-precipitation, the obtained dried HMG-CoA reductase inhibitor compound itself is mixed with the buffering substance or the basifying substance in a very homogeneous and finely distributed form. It is believed that the buffering substance or the basifying substance is finely distributed around the HMG-CoA reductase inhibitor crystals, thus forming a kind of protective xe2x80x9cmicroenvironmentxe2x80x9d. The protective effect is much more efficient as in the case of merely mixing or granulating starting powders, even in a wet process, as performed in EP-A-0 336 298. Moreover, since already the HMG-CoA reductase inhibitor as such (in bulk) is efficiently protected against deleterious environmental factors due to the excellent homogeneous distribution with the buffering substance or the basifying substance, the HMG-CoA reductase inhibitor can be handled more conveniently and stably stored as such, if desired, before being added to the pharmaceutical formulation. In particular, the homogeneous composition according to the present invention is highly resistant to the negative effect of carbon dioxide and moisture from the air, and a much better protection against low pH conditions is achieved when the composition containing the HMG-CoA reductase inhibitor is incorporated as the active substance into the final pharmaceutical formulation.
Accordingly, the present invention also makes available a newly stabilized pharmaceutical formulation comprising the aforementioned specific composition as the active substance.
According to the-present invention, there is further provided a process for preparing a stabilized HMG-CoA reductase inhibitor which comprises the step of crystallization and/or precipitation of the HMG-CoA reductase inhibitor with the buffering substance or the basifying substance.